1. Field of the Invention
The present invention relates to a control device of a direct injection internal combustion engine that sets injection start timing of an injector, which injects fuel into a cylinder of the internal combustion engine, and ignition timing of a spark plug such that injection end timing of the injector and the ignition timing of the spark plug have a predetermined relationship.
2. Description of Related Art
In recent years, as one of internal combustion engines mounted in vehicles, there has been a direct injection internal combustion engine having features of low fuel consumption, low exhaust emission, and high output at the same time. In the case of a certain direct injection internal combustion engine (for example, refer to Patent document 1: PCT application Japanese translation publication No. 2003-54186), an injection period of an injector is calculated from a required fuel injection quantity and injection start timing is set with a crank angle based on the injection period such that the injection ends at timing advanced from ignition timing of a spark plug by a predetermined crank angle when fuel pressure is higher than a predetermined value during starting.
The inventor of the present invention is studying a system that ends injection of an injector immediately before a compression top dead center and sets injection start timing and ignition timing such that ignition of a spark plug is performed at timing substantially the same as or immediately after injection end timing (that is, such that the ignition of the spark plug is performed at timing when a suitable stratified mixture gas is formed in the cylinder), thereby stabilizing a combustion state when operating a direct injection internal combustion engine in a compression stroke injection mode (i.e., a mode of injecting fuel into a cylinder in a compression stroke to perform stratified combustion of the fuel). During the study, a following new problem has been found.
Generally, the injection start timing of the injector and the ignition timing of the spark plug are set with the crank angle, but the injection quantity of the injector is set with the injection period (a valve opening period). Therefore, even if the injection start timing and the ignition timing are set with the crank angle beforehand to perform the ignition near the injection end timing as mentioned above, there is a possibility that the injection end timing (a crank angle at timing t1 when the injection period elapses after the injection start timing) deviates toward a delayed crank angle side from the preset ignition timing and the ignition is performed in the middle of the fuel injection (that is, in the middle of formation of a suitable stratified mixture gas in the cylinder) when rotation speed (crank angle speed) of the internal combustion engine rises abruptly during the starting or acceleration of the internal combustion engine as shown in FIG. 12. As a result, the combustion state worsens, causing a misfire and decrease in torque or increase in a HC emission quantity due to incomplete combustion. Such the problems can arise similarly in the technology described in Patent document 1 (that sets the injection start timing such that the injection ends at timing advanced from the ignition timing by a predetermined crank angle).